Fish Diversity Research Articles

FISH ABUNDANCE AND DIVERSITY AS BIOINDICATOR OF WATER QUALITY IN SENGGURUH AND KARANGKATES RESERVOIR

Reservoirs serve as beneficial recreation areas for the surrounding community. Reservoirs are also habitats for various types of flora and fauna. Severalfamous reservoirs in East Java due to their fisheries potential are Sengguruh and Karangkates Reservoirs. This study aimed to determine the abundance and diversity of fish as bioindicators of water quality in Sengguruh and Karangkates Reservoirs. Fish and water quality parameters weresampled at three points in each reservoir, namely residential, tourism, and fisheries areas. All data were analyzed descriptively, while the correlations between fish abundance and diversity with water quality were determined using the Pearson’s correlation test. According to the results, three fishfamilies were found in Sengguruh Reservoir with a relative abundance of 26 - 55 ind/200 m and a diversity index ranging from 1.6510 to 1.7239. Meanwhile, in Karangkates Reservoir, four fishfamilies were found with a relative abundance of 41-43 ind/m and a diversity index of 1.7806 - 1.8787. The water quality parameters showed temperature of26-28.7℃, pH of 7.5-8.5, DO of 4.5-8.2 mg/L, CODof 20-28 mg/L, ammonia of 0.18-0.77 mg/L, and nitrate of 6.7 - 21 mg/L. Based on the diversity index value, both reservoirs are classified as lightly polluted, with abundance variables have no correlation with temperature, yet negative correlation is presented with DO, pH, and nitrate. In contrast, a positive correlation is shown with phosphate and ammonia.

Ecological indicators for restoration success: Development of fish diversity in a large restored floodplain over twelve years

The restoration of rivers and their floodplains is complex, requires substantial financial efforts, intensive stakeholder involvement and long recovery times, making the identification of appropriate ecological indicators for restoration success a key challenge. Herein, one of the largest floodplain restorations along the European Danube was repeatedly assessed over a 12-year period. Changes in the fish community composition in relation to chemical and morphological habitat variables were assessed in all three restored habitat types free-flowing rivers (RS), reconnected oxbows (OS), and small floodplain ponds (FP) which are only temporarily connected to the main stem Danube. Fish species composition of RS, OS, FP and the Danube differed significantly. Species numbers (34 detected in 2022) remained largely constant since the last monitoring in 2013, whereas abundance increased by 15%. Small-bodied target species with short generation times were able to establish populations comprising all size classes shortly after restoration, whilst large-bodied species needed a decade after the restoration for full demographic representation. Highly specialised species such as the rheophilic Chondrostoma nasus used restored RS only during the life stages spawning and juvenile growth. Restoration increased habitat heterogeneity and the initialized hydromorphological processes are still ongoing, supporting the high species diversity. The observed differences in colonization patterns can be explained by species-specific life histories, resulting in diverse short and long-term responses of different fish species and life stages following restoration. Consequently, a comprehensive assessment of restoration success only becomes possible if multiple fish species as ecological indicators are combined in a long-term monitoring.

Environmental DNA as a novel tool for monitoring fish community structure and diversity feature in the northern Antarctic Peninsula

The northern Antarctic Peninsula (NAP), one of the fastest warming area around the Southern Ocean, hosts a large variety of endemic fish and is influenced by complex hydrography. However, the dynamics of fish diversity kept unclear and without monitoring. Monitoring of environmental DNA (eDNA) is a noninvasive, ecofriendly, and accurate approach for detecting aquatic organisms, including fish. In this study, the fish composition and diversity were detected by high-throughput sequencing of eDNA for the first time in the NAP. Overall, 32 species (1 order, 6 families, and 25 genera) of fishes were detected in the environmental water samples from 18 stations around the NAP, in which number of fish species were similar in the Drake Passage and the northern shelf of the South Shetland Islands (DP-SSIs) and the Bransfield Strait (BS). Most of the fish species were identified in previous Antarctic fish surveys using conventional methods, which supports the applicability of eDNA-based survey. Moreover, Pogonophryne albipinna was detected firstly in the NAP. Among the identified fish species, Champsocephalus gunnari and Notothenia rossii had the highest abundance (45.04% and 27.59%, respectively). There was difference in fish composition between the DP-SSIs and BS stations, although alpha diversity indices did not differ. The dissolved oxygen content and water temperature were the main drivers for the differences in fish species composition between areas. Our results indicated that eDNA could be a rapid and accurate biomonitoring approach for the entire Southern Ocean, particularly in areas with difficult logistics, in the future.

Beyond the Surface: Mesophotic Reefs as Potential Refuges for Shallow Fish Assemblages.

The deep reef refugia hypothesis suggests that the effects of disturbance decrease as depth increases; thus, reefs in the mesophotic zone potentially serve as refuges for communities in shallower zones. This study challenged this hypothesis by evaluating fish diversity in shallow and mesophotic reefs in a marine protected area in the Gulf of California. During 2021-2022, we conducted 189 5-min video transects using remotely operated vehicles to document species richness and abundance. We evaluated six biological traits for each species (length, mobility, position, gregariousness, diet, and activity period) to estimate four functional indices (number of entities, richness, originality, and divergence), one phylogenetic index (Δ*), and Hill's numbers for taxonomic and functional indices. Benthic organisms were analyzed to explore relationships with ichthyofauna, while monthly water turbidity satellite data products were transformed into a light attenuation coefficient to identify the mesophotic zone (area between 10% and 0.1% of the incident light at the surface). At the study site, the mesophotic zone was identified to extend to 21 m under optimal conditions, which is shallower than what is typically observed in oligotrophic regions. Generalized linear models revealed significant variations in reef fish composition across spatial (site and zone) and temporal (season and year) dimensions. Additionally, generalized linear mixed models of functional richness and taxonomic Hill's numbers exhibited significantly higher values in the shallow zone. However, functional and phylogenetic indices showed similarities in fish assemblages. Despite differences in fish taxonomic diversity among zones that could be related to less environmental variation and resource availability in deep strata, mesophotic reef fish assemblages presented similar functions. Functions were maintained in mesophotic reefs, which suggests that the two zones are connected and that mesophotic reefs have the potential to act as partial refugia in the face of current and near-future climate change-related disturbances that could affect shallow zones.

Seasonal distribution of fishes at nearshore meadows predominated by <i>Zostera marina</i> and <i>Ulva fenestrata</i> in the Stark strait (Peter the Great Gulf, Sea of Japan)

The fish species diversity, fish density, and distribution in the nearshore beds of Zostera marina and Ulva fenestrata have been assessed by SCUBA visual counts in May–September and November 2021. In total, 23 fish species have been registered. The fish species richness increases from 8–13 species in May to a maximum of 17–19 species at the end of June. Then it slightly decreases in July–September and reaches its lowest values in November (2–5 species). The same changes have been noted for the fish density. Fish diversity in the Zostera beds is higher than in the Ulva ones. The similarity of the fish species composition between Zostera and Ulva is low (the Sørensen-Czekanowski index varied from 0.32 to 0.44). In general, fish density is low (from 2.4 to 112.4 ind./50 m2 in Ulva (in November) and Zostera (in July) beds, respectively), although with an exception for Opisthocentrus spp. and Gymnogobius heptacanthus juveniles. An abnormal high bottom water temperature (above 26°C) in late July–early August has led to temporal avoidance of shallow water with plant beds by fishes (except for Gymnogobius heptacanthus) and their migration to a depth of 3.5–4.5 m, where the temperature was lower by 4.0–5.7°С.

Coexistence in long-term managed lakes: Limited evidence of negative impacts of invasive macrophytes on fish communities

Invasive macrophytes are widespread and can disrupt freshwater ecosystems if not properly managed. Their impact on fish is a topic of ongoing discussion, with studies reporting contrasting results. Utilizing datasets spanning 17 years of monitoring across 34 lakes in Florida, we examined the effects of the primary non-native invaders water hyacinth (Eichhornia crassipes (Mart.) Solms), hydrilla ((Hydrilla verticillata L. f.) Royle), and water lettuce (Pistia stratiotes L.), plus the entire non-native macrophyte assemblage and abiotic variables on fish species richness, Shannon diversity, abundance, length, and biomass. Together, these indicators help assess and manage the impact of invasive species and environmental changes on freshwater ecosystems. Our study was conducted at both habitat and lake scales to ensure a more thorough understanding of potential impacts. We found evidence of a marginally positive influence of hydrilla on fish species richness and abundance, a positive influence of water lettuce on Shannon diversity, and a positive effect of water hyacinth on fish length, all at the habitat scale. Notably, these effects were largely analogous to those of native macrophytes. Water temperature of about 26 °C and dissolved oxygen levels between 5 and 10 mg/L appeared to be optimal for fish. Lakes located in northwest Florida exhibited higher fish diversity and abundance. The integrated use of ecological indicators reveals that long-term management of lakes might limit populations of non-native macrophytes, thereby reducing the adverse effects of invaders on fish communities and facilitating their coexistence. This study highlights the importance of management strategies and long-term monitoring in minimizing the impacts of invasive plants on freshwater ecosystems.

EDNA metabarcoding reveals differences in fish diversity and community structure in Danjiang River

Fish diversity, an important indicator of aquatic ecosystem health, is declining due to water pollution, overfishing, climate change, and invasive species. Effective surveying and monitoring are required to protect fish diversity. Here, a high-sensitivity environmental DNA (eDNA) metabarcoding technique was used to investigate fish diversity in the Danjiang River, Shaanxi Province, China. In total, 59 species were identified in eight orders, 19 families, and 40 genera. Cypriniformes and Perciformes were the main groups in the survey area, while Cyprinidae accounted for 50.85% of the total fish species. Rhinogobius similis (19%), Hemibarbus umbrifer (11%), Gnathopogon herzensteini (10%), Triplophysa stewarti (8%), and Zacco platypus (7%) were the dominant species. Eight rare and two exotic fish species were identified. Combined with analysis of historical data, the richness of fish identified using eDNA metabarcoding was significantly higher than that of fish captured in ground cages. Temperature, pH, and oxidation-reduction potential are the main environmental factors that affect the spatial distribution of fish communities. These results suggest that eDNA metabarcoding could be a new tool with broad application prospects; however, local databases must be improved. This study provides theoretical data and a methodological reference for protecting and managing fish diversity in the Qinling Mountains.

Estuarine lateral ecotones shape taxonomic and functional structure of fish assemblages. The case of the Seine Estuary, France

Estuaries are complex ecotones including multiple lateral habitats that play essential functions for fish assemblages. However, the distribution of fish diversity and community assembly processes remain poorly documented in these habitats. This paper investigated the taxonomic and functional diversities of fish assemblages along lateral continuums of three salinity areas over the longitudinal gradient of the Seine Estuary. We examined fish diversity at a local scale (⍺-diversity) and between local scales (β-diversity) across the lateral habitats (estuarine main channel, tidal marsh, and diked marsh). Overall, the taxonomic diversity follows a typical ecotone distribution, with the highest richness reported at the system margins and high species dissimilarity between communities. The decrease of functional diversity in upper part of the lateral ecotone probably reflects the homogenisation of ecological niches. Changes in assembly processes between the three salinity conditions suggests that several lateral ecotones occur in estuaries with complementary functions for fish assemblages.

Distribution and Diversity of Coastal Fish in Fresh and Oligohaline Waters: An Example of the Largest Baltic Sea Estuary of the Neva River

ABSTRACTUnderstanding how low salinity gradients (0‰–5‰) influence fish life cycles is critical for clarifying principles of fish assemblage formation in estuarine ecosystems. This study is intended to provide a foundation for predicting changes in fish populations amidst ongoing surface salinity decreases in the Baltic Sea. In the Neva River Estuary, differences in fish diversity and distribution between fish assemblages in freshwater and oligohaline areas were assessed using beach seine and multi‐mesh gillnet surveys. The use of multiple sampling gears greatly enhanced understanding of fish distribution across salinity gradients. Fish assemblages were analysed depending on the different areas of the estuary, seasons of sampling, salinity and confounding environmental variables such as water temperature and depth. Salinity was the major influencing factor for the surf zone fish assemblages and a season of sampling was the main factor for coastal assemblages of larger fish studied with the gillnets. Fish assemblages in the surf zone exhibited significant but gradual changes in freshwater and marine‐estuarine fish occurrence and abundance along the critical oligohaline barrier ‘δ‐horohalinicum’ (0.5‰–1.9‰). Although freshwater species showed high occurrence and abundance throughout the estuary, their juveniles were less abundant in the oligohaline surf zone with salinity ≥ 2‰, where small‐size marine‐estuarine and euryhaline species predominated. Coastal multi‐mesh gillnet catches showed remarkable similarity between assemblages of larger fish in freshwater and oligohaline areas. Differences in species richness and diversity indices were not pronounced throughout the salinity gradient; the decline in freshwater species was offset by an increase in marine‐estuarine and euryhaline species.

Forage ecology of Neotropical fish in Brazilian biomes using stable isotopes

Neotropical regions are responsible for harboring most of the global diversity of freshwater fish, providing essential ecosystem services for society. Human activities (e.g., land use changes) jeopardize aquatic ecosystems as well as species, communities, etc., impairing ecosystem services. We investigate the impact of human disturbance on the foraging ecology of Neotropical freshwater fishes across five Brazilian biomes by stable isotope analysis. We analyzed carbon (δ13C) and nitrogen (δ15N) isotopic compositions of Neotropical fishes, sourced from the SIA-BRA dataset. Fishes were categorized into herbivores, omnivores, and carnivores. We tested the correlation between human disturbances, indicated by the human disturbance index (hdi), and changes in fish diets. We expected that the assimilation of C4‑carbon from exotic forage would increase with higher disturbance levels, while δ15N levels would similarly rise due to nitrogen input from anthropogenic sources. We found increases in fish δ13C with human disturbance increases, suggesting greater assimilation of C4 carbon in places where native vegetation was replaced by C4 sources, confirmed by isotopic mixing models. In contrast, δ15N values did not show a significant relationship with human disturbance, probably due to the complex interactions and multiple sources of nitrogen in disturbed environments. Our finds suggest that stable isotope analysis provides a powerful tool for monitoring the effects of landscape changes on aquatic food webs. Particularly, the δ13C values of detritivorous fish that feed on C4 plant detritus could serve as bioindicators of environmental degradation. However, a specific isotopic characterization of each site would be valuable for more accurate niche information.

Spatial and Temporal Diversity of Fishes at Wuzhizhou Island in the South China Sea Based on Environmental DNA

Spatial and Temporal Diversity of Fishes at Wuzhizhou Island in the South China Sea Based on Environmental DNA

The re-use of offshore platforms as ecological observatories

The high number of offshore platforms at the end of their productive phase offers the opportunity of their re-use and the development of effective management solutions, such as the possibility of utilizing them as ecological observatories for monitoring marine ecosystems and their biological resources. Here, through a multiparametric observatory deployed at an unproductive offshore platform, located in the Central Adriatic Sea (Mediterranean Sea), we collected data for 13 months on benthopelagic fish assemblage and habitat conditions. A total of 155.5 h of high-frequency (30 min) video-monitoring, recorded higher fish abundances during spring-summer periods during daytime, while fish diversity was highest in autumn. Some environmental variables contributed significantly to explain the overall community variance. Our results suggest that offshore platforms can be re-converted into ecological observatories, to collect relevant amounts of information that can be difficulty obtained with alternative approaches, contributing to our understanding of changes occurring in open water ecosystems.

Trends in fish diversity in Portuguese estuaries in the past decades and predictions in face of global changes

Coastal transition ecosystems like estuaries are amongst the most productive aquatic ecosystems on the planet, recognized worldwide as a fundamental component of coastal areas in terms of biological relevance and anthropogenic use. Estuaries along the Portuguese coast differ in their geomorphological and hydrological characteristics. These systems play a crucial role in terms of nursery areas for economically important fish species. Although several authors have observed high specific variability in estuarine fish communities along the Portuguese coast, few studies explore the factors that influence it. Most of these studies focus on a single estuary and, when several are addressed, only a single factor is used to assess the specific variability of the communities. The presente work aims to analyze the ecological role played by these estuaries for fish communities, namely in terms of their species richness, using a 30 year historical database provided by the Portuguese Coastal Monitoring Network Research Infrastructure (CoastNet RI). To this end, a generalized additive model (GAM) was developed to analyze the variation of species richness as a function of a set of temporal, spatial and environmental characteristics from the nine principal estuarine systems on the Portuguese coast. A total of 142 species from 45 families were identified. The Tejo, Mira, and Sado estuaries had the highest species counts (92, 72, and 64 species, respectively), while Minho and Ria de Aveiro had the lowest (26 and 27 species, respectively). The GAM model explained 35.1% of the variance in species richness and demonstrated significant differences in fish species richness in space (among the nine study estuaries) and time (at annual and monthly scales), and these differences were influenced by abiotic factors such as salinity and temperature. Species richness decreased with higher latitudes and varied yearly, showing a downward trend post-2002. Monthly variations showed increases in February–March and September–October. Higher species richness correlated with salinity levels between 25 and 37 and temperatures between 14 and 25 °C. Possible scenarios of future variations caused by the effects of climate change on the significant factors are also discussed. These GAMs could be useful as a preliminary tool to prepare long-term conservation plans for national legislation.

Comprehensive assessment of fish diversity and water health in river Indus, Khyber Pakhtunkhwa, Pakistan.

Fish diversity and water quality are vital indicators of the health of freshwater ecosystems, however these systems are increasingly threatened by environmental changes and anthropogenic activities. This investigation aimed to assess the fish diversity and evaluate the physicochemical parameters of water at Ghazi Swabi near Tarbela Dam, River Indus, Khyber Pakhtunkhwa, Pakistan, between March and June 2020. Monthly water samples were collected and analyzed for various physicochemical parameters such as temperature, dissolved oxygen (DO), total dissolved solids (TDS), pH, turbidity, salinity, and concentrations of heavy metals including lead (Pb), copper (Cu), cadmium (Cd), and mercury (Hg). Using various nets and traps the fish specimens were collected with the help of local fishermen. Morphometric and meristic analyses were conducted to identify the species, while systematic keys were used to remove misidentifications. A total of 110 fish specimens were collected, representing 7 species across 6 genera, 3 families, and 3 orders. The family Cyprinidae was the most abundant, with species including Puntius conchonius, Puntius waageni, Crossocheilus diplocheilus, Barilius modestus, and Aspidoparia morar. The Belonidae family was represented by Xenentodon cancila, and the Ambassidae family by Chanda nama. Physicochemical analysis showed that the water quality remained within permissible limits for aquatic life, however higher levels of certain heavy metals were detected, which may pose long-term risks. The study concluded that the fish diversity at Ghazi Swabi near Tarbela Dam reflects a moderately healthy ecosystem, the presence of heavy metals in the water raises concerns about future ecological health. Regular monitoring and mitigation efforts are recommended to preserve biodiversity and maintain water quality. The study suggests the need for sustainable management practices to protect freshwater ecosystems from anthropogenic impacts.

Community Diversity and Dynamics of Fish Assemblages in Lake Kanyaboli, Western Kenya

ABSTRACTAlthough Lake Kanyaboli provides a sanctuary for fish species that are considered extinct (e.g., Oreochromis esculentus, Oreochromis variabilis and Haplochromis spp.) in Lake Victoria, comprehensive data on species diversity and abundance are lacking. This study, conducted over a year (February 2020 to February 2021), addressed this gap by assessing the temporal variation in fish diversity, abundance and catch (biomass) in Lake Kanyaboli. The primary fish data collected in the lake were supplemented with secondary data, and physico‐chemical variables were used to correlate with fish assemblages. Fish catches decreased over time from 1981 to 2020, with the highest catch observed in 1981 (250 mt). Fish species composition data showed heterogeneity over the years, ranging from 9 to 15 species. O. esculentus, haplochromines, Oreochromis niloticus, Protopterus aethiopicus and Clarias sp. were present in all the reviewed years (from 1981 to 2020), whereas Coptodon zillii was non‐existent post‐1981 results. The February 2020 to February 2021 survey recorded 14 species dominated by Cichlidae (10 species), whereas Protopteridae and Anabantidae recorded one taxon each. Interestingly, Bagrus sp. was recorded in the current study, suggesting fish movement from the Yala River to the lake. The annual fish catch in the lake comprised tilapias (50%, O. esculentus, O. variabilis, O. niloticus and Oreochromis leucostictus), Clarias sp. (23%), P. aethiopicus (20%), haplochromines (7%), Cyprinids (0.03%) and Anabantidae (0.01%). There were no significant monthly differences in fish abundance and fish catches. The decline in fish catch in Lake Kanyaboli over the years is consistent with most tropical lakes and reservoirs in developing countries due to overexploitation. This study highlights the need for biomonitoring in Lake Kanyaboli to protect its fish population, including the endangered O. esculentus and O. variabilis, and ensure the long‐term sustainability of the ecosystem.

Weak integration allows novel fin shapes and spurs locomotor diversity in reef fishes.

In complex functional systems composed of many traits, selection for specialized function can induce trait evolution by acting directly on individual components within the system, or indirectly through networks of trait integration. However, strong integration can also hinder diversification into regions of trait space that are not aligned with axes of covariation among traits. As a result, non-independence among traits may limit capacity for functional expansion. We explore this dynamic in the evolution of fin shapes in 106 species from 38 families of coral reef fishes, a polyphyletic assemblage that shows exceptional diversity in locomotor function. Despite strong shared developmental pathways and expectations of a strong match between form and function, we find that species that share swimming mode show substantial disparity in fin shape, and preferred swimming mode is a poor predictor of fin shape. The evolution of fin shape is weakly integrated across the four functionally dominant fins in swimming (the pectoral, caudal, dorsal, and anal fins) and integration is weakened as derived swimming modes evolve. The weak integration among fins in the ancestral locomotor condition provides a primary axis of diversification while allowing for substantial off-axis diversification via independent trait responses to selection. However, the evolution of novel locomotor modes coincides with a loss of integrated axes of covariation among fins. Our study highlights the need for additional work on the functional consequences of fin shape in fishes and impact of evolutionary integration on functions other than locomotion.

The secret meal of Antarctic mesopelagic fish (Myctophidae: Electrona) revealed by multi-marker metabarcoding

IntroductionIn the Southern Ocean, myctophids are the most successful pelagic fish group in terms of diversity, biomass, and abundance. They play a crucial role in linking primary consumers and coupling carbon flux between surface and mesopelagic depths. Understanding their trophodynamics is key to assessing pelagic ecosystem resilience under environmental change. Conventional stomach content analyses indicate that myctophids predominantly feed on crustaceans, such as copepods and euphausiids, but are less effective at detecting easily digestible, soft-bodied organisms like gelatinous zooplankton (GZP) and pteropods. MethodsThis study used multimarker (COI Leray-XT and 18S v1-v2) DNA metabarcoding to analyze the diets of two abundant myctophids in the Scotia Sea, Electrona antarctica and Electrona carlsbergi.Results and discussionWe found a diverse diet dominated by copepods and euphausiids, followed by pteropods and GZP in terms of frequency of occurrence and relative read abundances. Within the GZP, salps and appendicularians were major components of the diet for E. carlsbergi, while hydrozoans were prominent in E. antarctica. With regards seasonal and spatial variability in the dietary contribution of GZP, E. carlsbergi consumed primarily appendicularians, chaetognaths, and hydrozoans during spring (2006) in the northern region, and more salps (predominantly Ilhea racovitzai) and other cnidarians in autumn (2009) in the southern region. Our study reveals the dietary diversity of myctophid fish as well as the importance GZP consumption as a key trophic pathway in the Southern Ocean.

Fish Diversity in a Little-Known Border River Between China, North Korea, and Russia, According to Traditional and eDNA Surveys

The Tumen River, which delineates the border between China, North Korea, and Russia, is a vital river in Northeast Asia. Understanding its current fish diversity holds significant scientific value for aquatic ecological protection. Therefore, traditional and eDNA sampling were conducted from 2022 to 2023. Integrating the historical literature with our field collection results reveals that the Tumen River has a total of 64 native fish species, of which 51 species have been surveyed in the wild. The fish composition is mainly dominated by cold-water species, with a high proportion of these being rare, endangered, and nationally protected. eDNA surveys are crucial complements in boundary rivers where traditional methods are not feasible. The results indicated that α diversity values were highest in the Hunchunhe River, attributed to the favorable natural geographical conditions and effective conservation efforts. Recently, the fish diversity in the Tumen River has been disrupted, primarily reflected in the absence of migratory species such as Oncorhynchus gorbuscha and Pseudaspius hakonensis. The study suggests that establishing nature reserves, preventing and controlling alien species, and strengthening international cooperation are key to protect fish diversity.

Comparison of Environmental DNA Metabarcoding and a Traditional Survey Method for Assessing Fish Diversity and Distribution Along Salinity Gradient in an Urban Brackish Reservoir, China.

With the decrease in fish diversity, the monitoring of fish has become a current research hotspot. Here, the fish diversity and spatial distribution along a salinity gradient (0.28‱-3.32‱) in Xinglinwan Reservoir, China, were investigated using eDNA and the TSM. With the combination of both methods, 12 species from 6 orders, 9 families, and 11 genera were observed. The invasive species Oreochromis niloticus had the highest relative abundance, accounting for 56.91% in the TSM and 89.80% in eDNA, respectively. eDNA detected 83.33% of the species detected using the TSM, and an additional six species (50.0% of the total species) were detected via only eDNA. Moreover, eDNA supplemented the unavailable abundance data from the TSM. The TSM revealed that the diversity and relative abundance of fish inhabiting seawater and brackish water increased with an increase in salinity, but this was not found using eDNA. Thus, our study highlights that Xinglinwan Reservoir has a low species richness and is suffering from the great harm of ecological invasion. Our findings also show that eDNA could be reliable for providing a comprehensive picture of fish, but discriminating the spatial heterogeneity of fish communities is a challenge for its widespread adoption in lentic brackish systems.

A bright spot of conservation in a Brazilian hotspot of cumulative impacts considering ecosystem quality in a cross-shelf gradient: Perspectives to MPAs network

Coastal regions are the main populated areas in the world and the effectiveness of Marine Protected Areas (MPAs) depends on management, stakeholder engagement, and environmental settings, which differ across land-to-sea gradients. This study describes the patterns of biological diversity and the abiotic environment along a densely inhabited stretch of the Brazilian coastline. We examined sea surface temperature and chlorophyll-a concentrations among urbanized coasts, inshore, and open water zones. Locally, we considered sites under contrasting protection status (partially restrictive MPA, multiple-use MPA, and no protection areas), the impact of sedimentation, the structure of sessile (algae, corals, and other invertebrates) and fish communities (abundance and diversity). Urban coastal sites are dominated by filamentous turfs (∼55 % coverage), exhibit high sedimentation rates (mean ∼180 mg/cm2/day), and low fish diversity (mean below 9 species/60m2). Open water zones have higher benthic and fish diversity. The highest biomass of fishes (mean ∼575 g/m2) as well as native corals (mean ∼13 %) and calcareous algal turf abundance (mean ∼38 %) was observed in the Alcatrazes archipelago, which increased its no-take MPA limits recently. In an unmanaged multiple-use protected Island, reefs were dominated by the invasive sun coral Tubastraea spp. The expansion of this alien coral is a real threat to the regional biodiversity, and its risk should be considered in management practices, which is done in the Alcatrazes archipelago. Our analysis demonstrates that effective management of multiple-use coastal settings may need to include flexible approaches that include land-based management, which can complement MPA tools to protect and conserve biodiversity. Since the region is considered a hotspot of cumulative impacts, ecosystem quality of the Alcatrazes archipelago could be considered substantially better than expected, being a bright spot of conservation. The expansion of its no-take area might help the role of MPAs within a comprehensive global conservation strategy.